Lead base alloy and cable sheath composed thereof



Patented Nov. 3,, 1942 LEAD. BASE ALLOY AND CABLE SHEATH COMPOSED THEREOF Gunnard E; Johnson, Hammond, Ind., and

William H. Bassett, Jn, Scarsdale, N. Y., as-

signersv to Anaconda Wire and New York, N.

No Drawing.

Cable Company,

Y., a corporation of Delaware Application December-13, 1940, Serial No. 310,000

4 Claims. (01. 75-166) This invention relates to lead-base alloys, and is concerned especially with the provision of a new and improved lead-base alloy suitable for use as a cable sheath material. The invention further contemplates the provision of a cable of the lead-sheathed type having a sheath formed of the new lead-base alloy.

Many electric cables of the lead-sheathed type contain oil as an insulating medium. In some such cables a channel is formed to permit the oil to flow freely in the cable, whereas in others the oil is impregnated into a solid but permeable insulation such as paper and so is relatively less free to flow in the cable. In all such cables, however, the oil can flow to some extent, and consequently when such cables are run vertically 'or at an angle to the horizontal, a hydrostatic pressure of oil develops in the lower part of the cable. This pressure must be resisted by the lead or lead alloy sheath. Commercially pure lead and lead alloys heretofore available have not proven very effective in resisting the hydrostatic pressure of the oil, especially in installations where such pressures are of considerable magnitude. On the contrary, cable sheaths of lead and lead alloys heretofore available have been subject in greater or lesser degrees to distension under prolonged, steadily exerted hydrostatic oil pressures, and many cases are known where the lead sheath ultimately has burst, ruining the cable.

We have discovered that if the sheath of an oil-insulated cable is formed of a lead-base alloy containing arsenic and bismuth in certain proportions, the bursting strength of the sheath is very much increased over that of sheaths formed of commercially pure lead or heretofore known lead-base alloys.

The lead-base alloys of the invention are composed of about 0.02% to 1% arsenic, about 0.02% to 1% bismuth, and the balance substantially all lead. (These percentages and others given elsewhere in this specification and in the appended claims are by weight of the alloy.) Alloys of arsenic in lead, and alloys of bismuth in lead, have been known for many years, but so far as we are aware, lead-base alloys containing both arsenic and bismuth in the proportions stated, with the balance substantially all lead, constitute a useful group of alloys not heretofore known.'

The presence of arsenic in the alloy of the in vention appears to have the effect of increasing its tensile strength and hardness appreciably,

while the bismuth improves the ductility of the alloy.

It has been found that of the alloys'containing arsenic and bismuth within the. range stated above, those containing about 0.1% to 0.2% arsenic and about 0.07% to 0.2% bismuth are particularly useful. Hardness, tensile strength, and

ductility are well developed in lead-base alloys containing arsenic and bismuth within these more restricted limits.

The following data indicate the valuable properties of the alloy of theinvention: The tensile strength of a commercially pure lead to which about 0.07% bismuth had been added was found to be about 1800 pounds per square inch at C., and its hardness was found to be about 20 on the Rockwell S scale. Upon the addition of a small quantity of arsenic amounting to about 0.02%, the tensile strength at 25 C. rose sharply to about 2300 pounds per square inch, and hardness on the Rockwell 8 scale also rose sharply to about 60. Increasing the arsenic content to I about 0.1% increased the tensile strength of the alloy at 25 C. to about 2600 pounds per square inch and the Rockwell S hardness to about 95. A still further increase in the arsenic content of the alloy to about 0.2% still further increased the tensile strength to about 2800 pounds per square inch at 25 C., and resulted in an increase in hardness to about 100 on the Rockwell S scale. With further increase in the arsenic con tent of the alloy up to about 1%, a further increase in tensile strength of the alloy at 25 C. to somewhat over 3600 pounds was obtained, and the Rockwell S hardness was increased to about 120. It will be noted that the rate of increase of both tensile strength and hardness becomes less as the amount of arsenic increases above about 0.2%.

In simple arsenic-lead alloys, increasing percentages of arsenic result in a decrease in the ductility of the alloy. By incorporating bismuth in the lead-arsenic alloy in accordance with the invention, however, the ductility ofthe alloy is much improved. For example, an alloy com-' posed of about 0.1% arsenic and the balance substantially all lead was found to have an elongation of about 35% in two inches at 25 C. The addition of 0.07% bismuth to this alloy brought about an increase in elongation to about in two inches at 25 C.

The alloy of the invention may be used with particular advantage as the material for the sheath of cables of the lead-sheathed type, particularly cables in which oil or other liquid insulating medium is employed. Such cables having a sheath formed of the new alloy are highly resistant to damage by distension or bursting of the sheath in consequence of the development of hydrostatic pressure of the oil or other liquid insulating medium in the cable. In general the alloys described above containing about 0.02% to about 1% arsenic, about 0.02% to 1% bismuth, and the balance substantially all lead may be used in accordance with the invention as the sheath for cables. Alloys within this range containing about 0.1% to 0.2 arsenic, about 0.07% to 0.2% bismuth, and the balance substantially all lead, are particularly useful as cable sheaths. These alloys are readily extruded by the conventional lead press used in the manufacture of ca ble sheaths.

Following are examples of improved results obtained using the new alloys in the manufacture of sheaths for cables of the lead-sheathed type. The life figures given below apply specifically to cylindrical cable sheaths having an outside diameter of about 2% inches and a wall thickness of about inch. A cable sheath composed of an alloy according to the invention containing about 0.16% arsenic and about 0.08% bismuth, upon exposure to a steady hydraulic pressure of 1500 pounds per square inch, had a life before bursting of approximately 66,200 minutes. A sheath composed of an alloy containing approximately 0.08% arsenic and approximately 0.09% bismuth, upon exposure to the same steadily applied pressure of 1500 pounds per square inch, had a life before bursting of approximately 64,000 minutes. Cable sheaths made from most of the commercial cable leads possess a life of only 100 to 500 minutes before bursting when subjected to internal pressures of 1500 pounds per square inch, and even high-strength lead alloys heretofore available, such as high-strength calcium leads, yield cable sheaths having little or no longer life at 1500 pounds per square inch than those made from the alloy of the invention. At pressures lower than 1500 pounds per square inch, cable sheaths made of the new arsenic-bismuth lead alloy are considerably longer-lived than cable sheaths of calcium lead, and much longer-lived than cable sheaths made from heretofore commonly available cable leads or lead alloys.

It has been observed that mechanical working of cable sheaths composed of the new alloy enhances their resistance to damage from internally applied pressure. Only relatively slight mechanical working is required to produce a cable sheath having a life of upwards of 100,000 minutes at 1500 pounds per square inch internal pressure. For example, a cable sheath composed of an alloy containing about 0.15% arsenic, about 0.17% bismuth, and the balance substantially all lead, possessed, before being mechanically worked, an indicated life of about 32,000 minutes under a pressure of 1500 pounds per square inch. A cable sheath of this same alloy, after being worked only to the extent of coiling it on a standard cable reel and thereafter removing it from the reel and straightening, showed a life of approximately 144,000 minutes upon test at 1500 pounds pressure.

Without limiting ourselves to any particular theory, it is our belief that the arsenic-bismuth lead-base alloys of the invention may be formed into cable sheaths having such long life at high pressures because the alloy is but slightly subject to mtercrystalllne deterioration and failure (similar to fatigue failure) which is noted in single arsenic-lead alloys and which is common in most other strong lead alloys.

It has been found that the presence of copper in the alloys of the invention is objectionable if the alloy is to be employed for use as a cable sheath. Even the presence of relatively small amounts of copper in cable sheaths composed of the new alloy has the effect of markedly lessening the expected life of the sheath when subjected to pressure. For example, an alloy containing approximately 0.1% arsenic, about 0.08% bismuth, about 0.02% copper, and the balance substantially all lead was found on tests to have a life of only about 18,000 minutes. For purposes of comparison, a cable sheath formed of an alloy containing approximately 0.1% arsenic and approximately 0.08% bismuth, when similarly treated and subjected to the same pressure, showed a life of approximately 64,000 minutes. In general the amount of copper present as an impurity in the new alloy should be less than about 0.025% if the alloy is to be used in the manufacture of cable sheaths.

In referring herein and in the appended claims to an alloy composed of arsenic and bismuth in the proportions set forth, and the balance substantially all lead, the expression "balance substantially all lead is intended to refer to commercial lead containing the usual small percentages of impurities, such as copper (less than 0.01%), silver, antimony, tin, zinc, and iron. The presence of such impurities in the small amounts in which they normally occur is not detrimental.

We claim:

1. A lead base alloy composed of about 0.02% to 1% arsenic, about 0.02% to 1% bismuth, and the balance substantially all lead,

2. A lead base alloy composed of about 0.1% to 0.2% arsenic, about 0.07% to 0.2% bismuth, and the balance substantially all lead.

3. A cable of the lead-sheathed type having a sheath formed of an alloy composed of about 0.02% to 1% arsenic, about 0.02% to 1% bismuth, and the balance substantially all lead.

4. A cable of the lead-sheathed type having a sheath formed of an alloy composed of about 0.1% to 0.2% arsenic, about 0.07% to 0.2% bismuth, and the balance substantially all lead.

GUNNARD E. JOHNSON. WILLIAM H. BASSE'I'I, Ja. 

